The basic rule of thumb with LA Weight Loss exchanges is the calories, carbs and fats. If the food you choose to exchange is not higher in those things then you're pretty much safe, however do keep in mind.....
1. The program is based on balance. If your exchanges short you on calories or carbs or even a food group too much, you may notice a decrease in weight loss.
2. You also have to keep the glycemic index in mind. If you exchange a lg veggie for a hg fruit, you may thwart your efforts to use stored fat.
3. From a results and nutritional standpoint....vegetables have more fiber for your body to break down, ergo, more energy is needed to do it, and more fat burned for that energy. In addition...you need that slow release of glucose to better support that protein you eat, to build more muscle. The more lean muscle you have, the better fat burner you are. Vegetables, especially raw vegetables are a very powerful tool in weight loss. They make your body work for it's calories and in turn you burn more fat to do it. If you hate them, at least learn to tolerate them lol.
Exchanges keep your diet interesting, but they are not always the optimum thing for it. I knew clients who ALWAYS chose 4oz of fruit juice to whole fruit. It showed in their results. Your body always does better when it has to work for it's nutrition. It's designed to break down and assimilate food. If you eat a lot of foods that are processed, defatted, denatured, lower in natural fiber and cellulose etc., on the short term you might see some results but your body needs to work for those calories...you will use and consequently lose more fat, and absorb ultimately more nutrients for your calories.
Remember this is not just about losing weight, it's about changing how you look at and deal with food and nutrition. That is what gives us lasting results.